This invention relates to the placement of cable within a conduit, and more particularly to a method and apparatus for performing such a cable placement, where placement is performed by drawing the cable through a conduit whereby such finally extends continuously through the conduit.
The invention has particular utility in connection with the placement of a cable or other elongate element within a conduit where the cable or element is tension-sensitive, in the sense that there is a limit imposed on the tension that may be applied to the cable or element in the placement operation. An example of such a tension-sensitive cable is so-called fiber optic cable, used in the communications industry. With such cable, manufacturers typically impose a limit on the maximum allowable tension that may be applied to the cable if manufacturing warranties are to be honored. Following the instant invention, a tension-sensitive element such as a fiber optic cable is placed within a conduit, not by pulling on such directly, but by pulling on a protective carrier belt which provides a protective sheath for the cable and which serves as a means for moving the cable through the conduit through a pulling force exerted on the belt rather than on the cable proper.
Further explaining the invention, and in particular its applicability to a fiber optic cable, the usual fiber optic cable is made up of a multiplicity of fine glass conductors serving to carry the information transmitted through the cable. Such conductors are relatively fragile, which has limited the amount of tension that may be applied to the cable in installing such in an underground conduit. Such a limit on tension has the direct result of limiting the length of cable that may be pulled through an underground conduit. With length restrictions present, increased costs are involved in cable installation, by reason of the greater number of vaults required to assist in the pulling operation, whereby such may be done without exceeding tension limitations. Furthermore, tension limitations result in the need for a greater number of fiber splices where one section of cable is spliced to another. Each splice generates a signal loss, with such losses accumulating throughout a project. Signal loss in turn impacts signal performance and so-called repeater/regeneration spacing. It should be obvious from this discussion that the provision of a method for installing relatively long lengths of a tension-sensitive element such as a fiber optic cable, without exceeding design-imposed tension limits on the cable, has very significant implications with respect to the cost of installing a line of cable, the performance of the cable once installed, and maintenance of the cable after installation.
Generally, therefore, it is an object of the invention to provide an improved method and means for positioning an elongate tension-sensitive element such as a cable within a conduit, which isolates the cable or element from the pulling force employed to produce the cable installation.
Another object is to provide an improved method and means for installing a tension-sensitive element such as a tension-sensitive cable within a conduit, which features an elongate continuous carrier belt that receives the cable on such entering the conduit, the belt within the conduit forming a protective sheath for the cable and the belt providing the medium through which a pulling force is applied when drawing the cable into and through the conduit.
Yet a further object is to provide a novel method of installing such a cable or element utilizing a carrier belt, which features the provision of an outer anti-friction surface contacting the inner wall of the conduit, and the introduction of lubricant between this friction surface and the inner wall of the conduit whereby the pulling force needed to draw a cable through a conduit is reduced.
In a preferred embodiment of the invention, the antifriction surface is characterized by elongate ridges and valleys extending the length of the outer surface of the belt. The valleys serve to channel lubricant along the belt, with such lubricant working its way between the outer surfaces of the ridges and the inner conduit wall that such contact.
A still further object of the invention is to provide a carrier belt usable in cable installation, made of stiff but pliable material, and which includes a pair of opposed elongate flap expanses which form an enveloping sheath for a cable on such being drawn through a conduit. Outer margins of these flap expanses move to close adjacency with the carrier belt and cable lodged within the conduit.
In a preferred embodiment of the invention, the flap expanses, with the carrier belt unstressed, have a shape where such at least partially extend about a passage or channel for receiving the cable. Such flap expanses, with deforming of the belt, may be moved away from each other to permit reception of the cable in the channel. Within the conduit which receives the cable and carrier belt, the flap expanses move into a more covering relationship with respect to the cable lodged within the belt.
The carrier belt contemplated may have elongate tension-resistant means extending therealong through which pulling force is applied. Preferably such tension-resistant means operatively connects with enveloping flap expanses of the carrier belt, in a region of the belt remote from where edges of the flap expanses cooperatively adjoin each other, with the carrier belt and cable assembly lodged within a conduit.
These and various other objects and advantages are attained by the invention, as will become more fully apparent from reading of the following description, which is to be taken in conjunction with the accompanying drawings, wherein: